It can predict levels of illness so accurately that one of the pilot sites, the Royal Berkshire Hospital, saved £400,000 in three weeks by rescheduling non-urgent operations and avoided sending an overflow of patients for private sector treatment during a flu epidemic.

But, despite glowing reports, the project has been without external funding since March. The Met Office has diverted £100,000 from its existing budget to keep it going till now.

The Treasury gave the Met Office £1.2 million over two years to run the project, in which 28 NHS trusts, plus GP call-out services and NHS Direct centres, supplied information about times and types of illnesses.

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Next week the Met Office will hold talks with the Department of Health to try to secure its future.

The project needs £200,000-£750,000 a year, depending on the scale on which the forecasting is to continue. Once perfected, hospitals would be expected to pay for it.

Mark Gibbs, the Met Office's head of health forecasting, said: "We are hoping to convince the Department of Health of the benefits this service can bring to the efficiency of the health service and, more importantly, to improving patient care."

The project has made several findings. A sudden drop in temperatures is followed by a dramatic increases in heart attacks three days later and strokes two days after that. Thunder is followed by a huge rise in asthma. Hip fractures peak in December with the first winter ice but are at their lowest in February when old people mostly stay indoors.

During the recent heatwave, hospitals which had enough advance warning of record temperatures were able to cancel leave to cope with the increased cases of chest pain.

A Met Office employee said: "We are 50 per cent to blame for this situation. We should have looked for future funding before the last lot ran out."

Heather Bunce, of the Royal Berkshire and Battle Hospitals NHS Trust, praised the system, saying: "By predicting troughs and peaks in weather-related illness and injury, this work gives us the appropriate information to respond confidently and flexibly to the immediate and anticipated weather."

A Department of Health spokesman said the project's reliability and value had to be assessed further before funding was allocated.

He added: "There are two external evaluations to look at the reliability and value of such workload forecasting for the NHS, following which the Department of Health will consider funding in this area."